Electrical condenser



Sept. 4, 1928. 1,682,811

A. L. TERRY. JR

ELECTRICAL CONDENSER Filed Oct. 1. 1924 [722/812 for i Patented Sept. 4,1928.

UNITED STATES ARTHUR Ii, TERRY,

JR, or WELLESLEY Hints, MASSACHUSETTS, ASSIGNOR 'ro wea- REN G. OGDEN,OF QUINCY, MASSACHUSETTS .ELECTBIGAL CONDENSER.

Application filed October 18, 1924. Serial No. 744,387.

Thisinvention relates to electrical condens- I ers, and moreparticularly to such condensers to be built into tuned radio frequencycircuits. The object of the invention is to provide an improved meansfor tuning two inducta-nces wherein two variable condensers of unequalcapacity may be operated mechanically, as a unit, to tune the twoinductances in such a manner that the two tuned circuits are keptsubstantially in resonance with each other through all settings and,that the tuning is substantially accomplished by manipulation ofa singlecontrol. It is impracticable to accomplish this result by merelyconnecting two variable condensers rigidly, as by mounting their rotorsupon the same shaft, because it is impracticable under ordinarymanufacturing conditions to produce in quantity precision instruments,i. e. variable condensers having identical capacity curves. It islikewise commercially impracticable to produce two inductances, whichconstitute the other elements of the tuned circuits, that are absolutelyidentical in their characteristics. The

' tuning of each circuit always is more or less affected by externalinfluences, such for example as the presence of neighboring currentcarrying wires and the like.

, According to this invention a variable balancing condenser of smallcapacity is provided, being so arranged that it may be utili'zed toestablish a state of perfect resonance between the two circuits whichare approximately tuned to each other by the two condensers, known to beof unequal value, whose rotors are operated by the common control. Thecapacity of the balancing condenser must be at least equal to themaximum difference between the capacities of the two main tuningcondensers at any setting of the latter, and in practice the balancingcondenser may conveniently be connected in parallel with one of the maintuning condensers which has one set of its plates sufliciently reducedin size so that its capacity at all settings is certain to be somewhatless than that of the other tuning condenser. The capacity of thebalancing condenser may conveniently be approximately twice thedifference between the capacities of the main tuning condensers at anysetting of the latter, thereby providing a margin of "adjustmentsutficient to balance inequalities between the two-tuned circuits,throughout the entire range of adjustment of the tuning condensers.

To the accomplishment of this object and such others as may hereinafterappear, as will readily be understood by those skilled in the art, theinvention comprises the features and combinations of parts hereinafterdescribed and then particularly pointed out in the appended claims.

The various features of the invention will best be understood from adescription of the preferred embodiment thereof illustrated in theaccompanying drawings, in which Fig. 1 is a plan of two tuningcondensers of unequal capacities provided with means for balancing theircapacities in accordance with the present invention, specifically theillus trated condensers may be used for tuning the secondary of theantenna coupling transformer and the secondary of the radiofrequencyamplifying transformer; and

Fig. 2 1s a vertical section taken on line.

2-2 of F ig. 1, looking in the direction of the arrows and showing thebalancing means ad justed to increase the capacity of theadjacent tuningcondenser.

In the embodiment of the invention illustrated in the drawing twovariable condensers 1 and 3, of any preferred commercial type but thecapacity of one being altered as hereinafter explained, are coupledtogether so as to form a single tuning unit for the two inductances thatare to be maintained in resonance thereby. i-

As illustrated the condenser 1 is supported in the usual framecomprising a pair of end plates 4 and 5 held in the desired spacedrelation, by through bolts 7 provided with spacing sleeves 9' interposedbetween the plates. Each of these spacing sleeves 9 includes a series ofwashers 11 interposed between the seven fixed plates 13, which composethe stator, having holes therein through which the bolts 7 extend.Adjustable relatively to the stator is the rotor, composed of six plates15, mounted on a rotatable shaft,,17journalled in bearings 19 and 21carried by the end plates 4 and 5 respectively. The rotor plates 15 areheld in proper spaced relation relative any rotorplate 15.

.which are a series the shaft 45 is rotated by means to the statorplates 13 by washers 23 mounted on the shaft 17.

The condenser 3 is generally similar to the condenser 1. being supportedin a frame comprising a pair of end plates 31 and 33 held in properspaced relation by through bolts 35 entered through spacing sleeves 37interposed between the end plates 31 and 33. These sleeves include aseries of washers 39 between of seven fix-ed plates 41, which comprisethe stator having holes therein through which the bolts 35 extend.Similarly to the condenser 1, the condenser '3 is provided with anadjustable rotor, comprised of six plates 43, mounted on a rotatableshaft j ournalled in bearings L7 and 49 mounte in the end plates 31and33 respectively. The rotor plates 43 are held in proper spacedrelation relative to the stator plates 11 by a series of washers 51 onthe shaft 45. A very material difference between the rotors of the twoillustrated condensers will presently be described.

In the present instance of the invention, the two main condensers 1 and3 may conveniently be coupled together, so as to be under a singlecontrol, by through bolts 53 entered through the adjacent end plates 5and 31, the two condensers being held apart by sleeves 55 through whichthe bolts extend to'provide space between them for a coupling 57 secureto the abutting ends of the shafts 17 and 15. With this constructionboth rotors are adjusted to equal angular positions whenever of theusual The shaft 17 is provided 25 adapted to engage one and 29projecting dial fixed thereon. with a radial pin or another of the stops27 inwardly from end plate 5. thereby to limit the rotative movement ofboth rotors when ositioned either wholly within or wholly without thefield of their respective stators.

In carrying out the object of the invention each of the six rotor plates13 of the condenser 3 has an area substantially less than anyrotor plate15 of the condenser 1. As illustrated by Fig. 2 each rotor plate 13 isseen to have about eleven-twelfths of the area of This constructionmakes certain a substantial difference between the several capacities ofthe two variable condensers and provides two condensers of a knownpredetermined unequal value. Furthermore, the difference in capacitiesis so -material that the capacity curve of the condenser 3, remainsbelow the capacity curve of the condenser 1 at all settings. It ishighly important to the present invention that, when plotted, thecapacity curves of the two condensers show that the ordinates of onecurve are consistently somewhat less than the ordinates of the other. Inother words, the two capacity curves are such that for any commonabscissa, that is, for any like setting of the two condensers whentuning, the corresponding ordinates of the two curves will never beequal. More than this, the capacity curves will'not cross each other, asmay be true of two condensers taken at random from stock. Briefly, onecondenser is certain to be of somewhat less capacity than the other forany tuning adjustment.

' To balance, or compensate for, this difference in the capacities'ofthe two condensers so that when operated mechanically as a unit the twocircuits may be tuned identically or in resonance, a balancing condenser58 is provided. This balancing condenser is assofciated with thecondenser 3, of reduced capacity, and comprises an end plate 59, opposedto the end plate 13, mounted on the through bolts 35 which are extendedforwardly for this purpose. Fixed plates 61, forming the stator of thecondenser 58 have holes through which the bolts 35 project, said platesbeing held'in proper spaced relation by washers 63 on said. bolts. Sincethe required capacity of the balancing condenser is small, two statorplates 61 are sufficient. Between the stator plates 61 is an adjustablerotor comprising a single plate 65, mounted on a sleeve shaft 67supported by the shaft 45 and journalled in a bearing 69 carried by theend plate 59. The rotor is held spaced relative to fixed plates 61 by apair of washers 71 mounted on the sleeve shaft. The balancing condenserjust described may be the ordinary three plate socalled Vernier, and isso illustrated.

It will be observed that both the sleeve shaft 67 and the solid shaft 45project forwardly beyond theend plate 59 a sufficient distance to passthrough the panel board and receive dials or other means enablingrotation of said shafts and adjustment of the rotors supported thereby.

The rotor plate 65 of the balancing condenser is simllar to the rotorplates 15 of tuning condenser 1 and hence the capacity of the balancingcondenser is sufficient to b the two main tuning condensers to a likevalue with a sufficient margin of safety. It is obvious that thecapacity of the balancing condenser must be at least equal to thedifference in capacity of the condensers 1 and 3 that is produced bycutting off one-twelfth. of each of the six rotor plates 43 of condenser3 i. e. a total reduction in area equal to one-half of a single plate.In orderto provide a margin or adjustment sufficient to compensate foror balance inequalities between the two tuned circuits throughout theirentire ranges of adjustment'the illustrated balancing condenser (seeFig. 2) has a capacity of approximatel twice the difference between thecapacities oi the two main tuning condensers. By mak ing the total areaof the rotor plates of one o the main tuning condensers substantiallyles than the total area of the rotor plates of th other main tuningcondenser, a suiiicien difference in the capacities of the two cordensers is established to enable this differ ence to be compensated forby the balancing condenser with fine adjustment.

By means of this invention there is pro vided a simple and efficientconstruction whereby two condensers of unequal capacity,

connected for control from a single dial, may be perfectly balanced. Thesimplicity of tuning will be understood from the following. If thedifference in the length of the ordinates of the two capacity curves atdifier ent settings of the two tuning condensers is substantiallyconstant, then one initial setting of the variable balancing condenserwill be suflicient for the entire range of adjustment. The two circuitscan be accurately tuned to all other wave lengths by an adjustment ofthe single condenser-shaft. If the difference in length of saidordinates varies, for example bybecoming consistently greater or less asthe two circuits are tuned for higher wave lengths, then this variation.for the sharpest tuning, may be compensated for by a further adjustmentof the balancing condenser which in any event will be extremely slight.

Those skilled in the art will recognize that in this construction thereare really but two variable condensers, one having an unva-' riablecapacity cum 0. and the other having a capacity curve the shape of whichcan be varied slightly. By means of this invention absolute accuracy isobtained with condensers that are not accurately made. It is within thescope of the invention to provide any suitable means for transmittingrotation from one condenser shaft to the other.

While it is preferred to employ the specific construction andarrangement of parts shown and described it Will be understood that thisconstruction is not essential except so far as specified in the claims,and may be changed or modified without departing from the broaderfeatures of the invention.

What. is claimed as new, is

1. The combination of two tuning cone densers operated mechanically as aunit, one of which has a value less than the other at all settings, anda variable balancing condenser having a value equal at least to themaximum difference in value between said two tuning condensers andconnected in parallel with the tuning condenser of lesser value.

2. The combination of two tuning condensers operated mechanically as aunit, one

of which has a value less than the other at all settings, and a variablebalancing condenser having a value of approximately twice the maximumdifference in value between said two tuning condensers and connected inparallel with the tuning condenser of lesser value.

3. The combination oftwo variable tuning condensers, said condensershaving unequal capacities for all settings, means for operating saidcondensers as a unit, and

means .for compensating for the inequality in the\capacities of saidcondensers at all the se-ttlngs thereof.

4. The combination of a pair of variable tuning condensers connected tobe operated mechanically as a unit, each comprising a stator and anadjustable rotor, said stators being of like area but the rotor of oneof 'rotors of the tuning condensers.

5. The combination with two tuning condensers, each comprising fixed andadjustable plates, each of the adjustable plates of one of thecondensers having a portion removed to make certain that there is asubstantial difference in capacity between the two condensers, of abalancing condenser adjustable to compensate for the capacitydiii'erence between the condensers at all settings thereot, and meansfor adjusting said two tuning condensers as a unit and said balancingcondenser individually.

6. The combination with two variable condensers having stator platesequal in number and area and rotor plat-es .equal in number butsubstantially unequal in area, common means for adjusting saidcondensers to approximately tune two equal inductances, and adjustablemeans co-operating with the variable condenser of lesser capacityoperable to increase its capacity to equal that of the other Variablecondenser for any tuning adjustment thereof.

7. In combination, two variable tuning condensers of a predeterminedunequal value and mounted in parallel, a common adjusting shaft for the'respective rotorsthereof wherebythe capacities of said two condensersmay be simultaneously varied by a single control, a balancing condenseralso in parallel and adjacent the tuning condenser of lesser value, anda rotary adjusting sleeve on said shaft for the rotor of said balancingcondenser,wl1ereby the capacity of the con- 9. The combination of twotuning condensers,mechan1cal means for operating sald condensers as aunit,

said condensers having unequal capacities at all settings. and variablemeans for compensating for the inequality in the capacities of saidcondensers for all positions of said mechanical means.

10. The combination of two tuning condensers operated mechanically as aunit, one

ARTHUR Ln TERRY, JR.

